Various kinds of processing machinery are available for processing negative film, for processing colour prints, for processing colour reversal film and for preparing reversal prints.
In general the process involves developing a silver image then oxidising the silver in a bleaching stage followed by removimg the silver in a fixing stage. These stages occur in all normal photographic processes, whether black and white, or colour and whether negative or reversal processing; although further stages will be required in the case of reversal processing, and dye coupling during development in the case of colour processing.
In automatic processing systems, ingredients are taken up in the various stages of processing, and therefore the various processing baths need replenishment of their constituents in order to keep them at the correct consistency.
Automatic replenishment systems have been proposed previously in which the strength of the developed dye image is measured and this is then used to determine the rate of replenishment of the various ingredients. U.S Pat. Nos. 4,057,818 and 3,554,109 describe such systems.
In these systems dye density is measured after the film is fully processed in order to assess the replenishment needs.
These methods therefore give rise to a degree of inaccuracy since the amount of dye in the final image is not necessarily a direct function of the total amount of developing agent consumed in forming the final image.
The present invention directs itself to this problem and aims to provide an improved method of assessing the replenishment need.